The ancient world was full of strange animals that have gone extinct , such as a group of marine species with claw-like structures emerging from their heads . A new study suggests that these creatures were related to spiders and scorpions .

Researchers discovered the fossilized remains of a species in southwest China that provides new insights into the evolution of animals in the modern era , scientists said . They report their findings in the journal Nature .

Scientists believe that the creature -- 1 inch long , and with two pairs of eyes -- lived 520 million years ago and that it crawled or swam in the ocean . They were able to reconstruct the creature 's nervous system to gain insights about its evolutionary relationships to animals familiar to us .

`` For the first time , we are able to use fossilised neural anatomy to sort out how fossil animals are related to animals today , '' study co-author Xiaoya Ma of the Department of Earth Sciences at the Natural History Museum in London wrote in an e-mail .

This creature belongs to the Alalcomenaeus genus , and its place in the animal kingdom lies in `` a group of weird extinct animals '' called the `` megacheiran '' or `` great appendage '' arthropods , Ma said .

The species of the Alalcomenaeus group had elongated , segmented bodies with about 12 pairs of appendages they used for swimming or crawling . They also had a pair of long , scissor-like head claws , most likely for grabbing or sensing .

Scientists say the reconstruction of the new creature 's nervous system is the most complete for an arthropod living at that time , in the Cambrian geological period .

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The brain and central nervous system of the creature are organized in a way that is similar to those of the chelicerata , the group that includes horseshoe crabs and scorpions . This suggests a close evolutionary relationship between the ancient Alalcomenaeus and the living chelicerata .

A distinct group of arthropods called the mandibulates includes lobsters , insects , centipedes and millipedes .

Last year at the same site in China -- called the Chengjiang formation near Kunming -- Ma and colleagues discovered a 520 million-year-old crustacean-type nervous system in an animal called Fuxianhuia .

Taken together , these discoveries suggest that by 520 million years ago , the two major groups of arthropods had diverged . Their common ancestor must have been older , researchers said .

`` This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans , '' co-author Nick Strausfeld , neuroscience professor at the University of Arizona , said in a statement .

Strausfeld 's team used sophisticated imaging techniques to look at the inch-long Alalcomenaeus fossil . One kind of scan revealed that iron had built up in the nervous system as the creature fossilized . They also used a technique called computed tomography that reconstructs 3-D features .

By combining these images and discarding any data that were n't in both , they were able to create a sort of negative X-ray photograph , `` and out popped this beautiful nervous system in startling detail , '' Strausfeld said .

It confirmed what scientists had believed from the creature 's outward appearance : The extinct genus Alalcomenaeus was related to chelicerates -LRB- spiders , scorpions and others -RRB- .

They also saw that the brain in the fossil was like the brains found in modern scorpions and spiders .

If researchers find a fossil with features shared by this creature and the crustacean-like fossil Ma and colleagues found last year , that could be a common ancestor of both .

There 's plenty more weirdness from ancient history to uncover .

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The fossil is 520 million years old and was found in China

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Using multiple images of the animal , the researchers discovered the nervous system

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They also saw the brain was like those of today 's spiders , scorpions

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The work shows the early evolutionary differences , researcher says